1. Field of the Invention
The present invention relates to a polyaniline (material or film) which may be suitably used as an electronic material, particularly as an electrode material in a cell, photoelectric cell and the like, a process for the preparation of such a polyaniline, and a cell using it.
2. Description of the Prior Art
Recently, various studies of secondary cells using an electroconductive polymer as an electrode active material have been made in order to lighten the weight of such a cell. Among such cells, in particular, a secondary cell using a polyaniline as an electrode active material is known as a "conductive polymer cell" having good charge-discharge efficiency.
However, all the conventional cells using a polyaniline electrode were of laboratory scale and far from practical. The major reason is, according to the findings of the present inventors, that the thickness of such a polyaniline electrode formed on a current collector of platinum or the like was at most on the order of tens of microns.
In order to provide a practically available spiral or laminated electrode, it is necessary to form a polyaniline film having a thickness of the order of a few millimeters. However, such a thick film of polyaniline could scarcely have been provided.
Polyanilines for use as cell electrodes are generally prepared by oxidative polymerization of aniline in an aqueous acidic solution such as sulfuric acid etc.; while on the other hand a polyaniline synthesized in an alkaline solution is electrochemically inactive and cannot be utilized as an active material for a cell.
The oxidative polymerization of aniline is carried out either by using a chemically oxidizing agent such as persulfuric acid or by electrolytic oxidation.
In chemical oxidation, polyanilines are usually produced in a powdery form. The polyanilines should be used to form an electrode integrated with a collector, for example, by applying the polyaniline powder onto the collector and pressing, or by mixing the polyaniline powder with a binder and applying the resulting paste on the collector. Such an electrode is inferior to that of the polyaniline prepared by electrolytic oxidation with respect to the productivity, and energy density (discharge current and voltage), etc..
In electrolytic oxidation or polymerization, on the other hand, polyanilines are produced on an anode in the form of a film, and the whole polyaniline film can effectively be utilized as an electrode. Further, such an electrode has a low internal resistance, and therefore, the voltage decrease will be small. Thus, the electrode using the polyaniline prepared by the electrolytic polymerization will give a high energy density and is preferred for an electrode of a cell.
As stated previously, however, only thin films on the order of tens of microns have heretofore been provided even in electrolytic polymerization, since a film of polyaniline produced on an anode becomes brittle as the film thickness increases.